Sumana Paul

Tailored bifunctional polymer for plutonium monitoring.

Monitoring of actinides with sophisticated conventional methods is affected by matrix interferences, spectral interferences, isobaric interferences, polyatomic interferences, and abundance sensitivity problems. To circumvent these limitations, a self-supported disk and membrane-supported bifunctional polymer were tailored in the present work for acidity-dependent selectivity toward Pu(IV). The bifunctional polymer was found to be better than the polymer containing either a phosphate group or a sulfonic acid group in terms of (i) higher Pu(IV) sorption efficiency at 3-4 mol L(-1) HNO3, (ii) selective preconcentration of Pu(IV) in the presence of a trivalent actinide such as Am(III), and (iii) preferential sorption of Pu(IV) in the presence of a large excess of U(VI). The bifunctional polymer was formed as a self-supported matrix by bulk polymerization and also as a 1-2 μm thin layer anchored on a microporous poly(ether sulfone) by surface grafting. The proportions of sulfonic acid and phosphate groups in both the self-supported disk and membrane-supported bifunctional polymer were found to be the same as expected from the mole proportions of monomers in polymerizing solutions used for syntheses. α radiography by a solid-state nuclear track detector indicated fairly homogeneous anchoring of the bifunctional polymer on the surface of the membrane. Pu(IV) preconcentrated on a single bifunctional bead was used for determination of the Pu isotopic composition by thermal ionization mass spectrometry. The membrane-supported bifunctional polymer was used for preconcentration and subsequent quantification of Pu(IV) by α spectrometry using the absolute efficiency at a fixed counting geometry. The analytical performance of the membrane-supported-bifunctional-polymer-based α spectrometry method was found to be highly reproducible for assay of Pu(IV) in a variety of complex samples.

Thin extractive membrane for monitoring actinides in aqueous streams.

Alpha spectrometry and solid state nuclear track detectors (SSNTDs) are used for monitoring ultra-trace amount of alpha emitting actinides in different aqueous streams. However, these techniques have limitations i.e. alpha spectrometry requires a preconcentration step and SSNTDs are not chemically selective. Therefore, a thin polymer inclusion membrane (PIM) supported on silanized glass was developed for preconcentraion and determination of ultra-trace concentration of actinides by α-spectrometry and SSNTDs. PIMs were formed by spin coating on hydrophobic glass slide or solvent casting to form thin and self-supported membranes, respectively. Sorption experiments indicated that uptakes of actinides in the PIM were highly dependent on acidity of solution i.e. Am(III) sorbed up to 0.1 molL(-1) HNO₃, U(VI) up to 0.5 molL(-1) HNO₃ and Pu(IV) from HNO₃ concentration as high as 4 molL(-1). A scheme was developed for selective sorption of target actinide in the PIM by adjusting acidity and oxidation state of actinide. The actinides sorbed in PIMs were quantified by alpha spectrometry and SSNTDs. For SSNTDs, neutron induced fission-fragment tracks and α-particle tracks were registered in Garware polyester and CR-39 for quantifications of natural uranium and α-emitting actinides ((241)Am/(239)Pu/(233)U), respectively. Finally, the membranes were tested to quantify Pu in 4 molL(-1) HNO3 solutions and synthetic urine samples.

Chemically selective polymer substrate based direct isotope dilution alpha spectrometry of Pu

Quantification of actinides in the complex environmental, biological, process and waste streams samples requires multiple steps like selective preconcentration and matrix elimination, solid source preparations generally by evaporation or electrodeposition, and finally alpha spectrometry. To minimize the sample manipulation steps, a membrane based isotope dilution alpha spectrometry method was developed for the determination of plutonium concentrations in the complex aqueous solutions. The advantages of this method are that it is Pu(IV) selective at 3M HNO3, high preconcentration factor can be achieved, and obviates the need of solid source preparation. For this, a thin phosphate-sulfate bifunctional polymer layer was anchored on the surface of microporous poly(ethersulfone) membrane by UV induced surface grafting. The thickness of the bifunctional layer on one surface of the poly(ethersulfone) membrane was optimized. The thickness, physical and chemical structures of the bifunctional layer were studied by secondary ionization mass spectrometry (SIMS), scanning electron microscopy (SEM) and SEM-EDS (energy-dispersive spectroscopy). The optimized membrane was used for preconcentration of Pu(IV) from aqueous solutions having 3-4M HNO3, followed by direct quantification of the preconcentrated Pu(IV) by isotope dilution alpha spectrometry using (238)Pu spike. The chemical recovery efficiency of Pu(IV) was found to be 86±3% below Pu(IV) loading capacity (1.08 μg in 2×1 cm(2)) of the membrane sample. The experiments with single representative actinides indicated that Am(III) did not sorb to significant extent (7%) but U(VI) sorbed with 78±3% efficiency from the solutions having 3M HNO3 concentration. However, Pu(IV) chemical recovery in the membrane remained unaffected from the solution containing 1:1000 wt. proportion of Pu(IV) to U(VI). Pu concentrations in the (U, Pu)C samples and in the irradiated fuel dissolver solutions were determined. The results thus obtained were found to be in good agreement with those obtained by conventional alpha spectrometry, biamperometry and thermal ionization mass spectrometry.

Effects of neutron irradiation on optical and chemical properties of CR-39: Potential application in neutron dosimetry.

Effects of high-dose neutron irradiation on chemical and optical properties of CR-39 were studied using FTIR (Fourier Transform Infrared) and UV-vis (Ultraviolet-Visible) spectroscopy. The primary goal was to find a correlation between the neutron dose and the corresponding changes in the optical and chemical properties of CR-39 resulted from the neutron irradiation. The neutrons were produced by bombarding a thick Be target with 22-MeV protons. In the FTIR spectra, prominent absorbance peaks were observed at 1735cm(-1) (C=O stretching), 1230cm(-1)(C-O-C stretching), and 783cm(-1)(=C-H bending), the intensities of which decreased with increasing neutron dose. The optical absorbance in the visible range increased linearly with the neutron dose. Empirical relations were established to estimate neutron doses from these optical properties. This technique is particularly useful in measuring high doses, where track analysis with an optical microscope is difficult because of track overlapping.

Isotope dilution gamma spectrometry for Pu using low energy photons

Abstract Isotope dilution gamma spectrometry (IDGS) for determination of the Pu concentration, using high resolution gamma-ray spectrometry (HRGS) in the 40–150 keV energy range, is developed and described. The methodology involves purification of Pu by an anion exchange procedure, followed by the determination of Pu isotopic composition using HRGS. For isotope dilution, a pre-calibrated power reactor grade Pu (∼ 70 at. % 239Pu) solution from an Indian PHWR was used as a spike for research reactor grade Pu (∼ 95 at. % 239Pu) samples and vice versa. Changes in 240Pu/239Pu (45.24 keV/51.62 keV) and 241Pu/239Pu (148.57 keV/129.29 keV) activity ratios in the spiked samples were determined by gamma spectrometry. Using the atom ratios calculated from the measured activity ratios, the concentration of Pu in the sample was calculated using two different efficiency calibration methods. The isotopic composition and concentration of Pu samples both from power reactor and research reactor grade agreed well with the values obtained by isotope dilution-thermal ionization mass spectrometry. The present method also shows the superiority of using the 240Pu/239Pu atom ratio against the 241Pu/239Pu atom ratio in IDGS with respect to the accuracy and precision.

Effects of high neutron doses and duration of the chemical etching on the optical properties of CR-39.

Effects of the duration of chemical etching on the transmittance, absorbance and optical band gap width of the CR-39 (Polyallyl diglycol carbonate) detectors irradiated to high neutron doses (12.7, 22.1, 36.0 and 43.5 Sv) were studied. The neutrons were produced by bombardment of a thick Be target with 12 MeV protons of different fluences. The unirradiated and neutron-irradiated CR-39 detectors were subjected to a stepwise chemical etching at 1h intervals. After each step, the transmission spectra of the detectors were recorded in the range from 200 to 900 nm, and the absorbances and optical band gap widths were determined. The effect of the etching on the light transmittance of unirradiated detectors was insignificant, whereas it was very significant in the case of the irradiated detectors. The dependence of the optical absorbance on the neutron dose is linear at short etching periods, but exponential at longer ones. The optical band gap narrows with increasing etching time. It is more significant for the irradiated dosimeters than for the unirradiated ones. The rate of the narrowing of the optical band gap with increasing neutron dose increases with increasing duration of the etching.

Superparamagnetic bi-functional composite bead for the thermal ionization mass spectrometry of plutonium(IV) ions

Single resin bead-based thermal ionization mass spectrometry (TIMS) offers numerous advantages for Pu(IV) determinations in complex aqueous samples. These include removal of the matrix and interfering ions by a one-step process, selective preconcentration of Pu(IV) ions with a high chemical recovery, transportation without heavy shielding, avoiding the possibility of cross-contamination, and acting as a point source. The single-bead TIMS method reported in literature is based on an anion-exchange resin that lacks sorption-selectivity toward Pu(IV) ions, and where the beads are not easily retrievable from a large volume sample. Therefore, silica-coated superparamagnetic Fe3O4 embedded functionalized porous poly(ethersulfone) (PES) beads were developed for Pu(IV) preconcentration and analysis by TIMS. The beads were functionalized with a phosphate bearing monomer along with or without a quaternary ammonium bearing monomer by UV-induced surface grafting. Since the beads were used in a highly acidic solution, the Fe3O4 nanoparticles were protected with a silica coating formed by the hydrolysis and condensation of tetraethoxysilane. The PES porous beads were prepared by a phase inversion method. The monomers used for UV-grafting were 2-hydroxyethyl methacrylate ester and (3-acrylamidopropyl) trimethylammonium chloride. The functionalized beads were characterized by scanning electron microscopy, energy dispersive analysis, and vibrating sample magnetometry. The sorption studies indicated that the bi-functionalized PES beads consisting of phosphate and quaternary ammonium groups not only have a higher distribution coefficient (Kd) for Pu(IV) but also high selectivity toward Pu(IV) ions in the presence of a large excess of U(VI) ions (Kd(Pu(VI))/Kd(U(IV)) = 11.5). The phosphate-functionalized PES beads showed comparable selectivity (Kd(Pu(VI))/Kd(U(IV)) = 9.1), but a lower Kd value for Pu(IV). The quaternary ammonium-functionalized PES beads were found to have lower selectivity and Kd values toward Pu(IV) ions. The analytical performance of single bi-functionalized bead-based TIMS for the determination of Pu(IV) using isotope dilution was compared with the solution-based TIMS, validated using the Pu isotopic standard reference material NIST SRM-947 and applied to real samples such as dissolver solutions and soil leach liquors.

Polymer based sorbent materials for thermal ionization mass spectrometric determination of uranium(VI) and plutonium(IV) ions

Thermal ionization mass spectrometry (TIMS) is a widely used method for obtaining information about the isotopic composition of individual isotopes with high resolution and accurate quantification with considerably low detection limits. However, analyses by TIMS require an elaborate sample preparation step to eliminate the matrix and subsequent manual loading of small volumes of purified aqueous samples on a filament surface for thermal ionization. This is cumbersome, particularly for the handling of radioactive solutions. Therefore, in the present work, polymeric material based sorbents were explored for the single step matrix elimination and source preparation for the loading of U(VI) and Pu(IV) ions preconcentrated from a variety of environmental and nuclear fuel reprocessing samples. The solid phase loading offers a number of advantages for handling radioactive materials, and is amenable to matrix elimination and preconcentration of analytes that would further improve the detection limit of TIMS. The polymer based sorbents were prepared by anchoring neutral and acidic phosphate functional groups selective to actinide ions in porous poly(propylene) and poly(ethersulfone) matrices. One of the procedures used for the preparation of polymeric sorbents involved grafting of the monomers phosphoric acid 2-hydroxyethyl methacrylate ester and 2-ethylhexylmethacrylate (EHM) in 1 : 1 molar proportion by UV-initiator induced polymerization in the pores of the host matrix. In another route, the liquid extractants tris(2-ethylhexyl) phosphate (TEHP) along with bis(2-ethylhexyl) phosphoric acid (HDEHP), in different molar proportions, were physically immobilized by capillary force in the pores of poly(propylene) and poly(ethersulfone) membranes and beads. It was observed that the poly(propylene) pyrolyzed easily at a filament temperature close to that used for solution based sample loading, and thus was best suited for the analyses of U(VI) and Pu(IV) by TIMS. The composition of the polymer membrane supported liquid extractant based sorbents was optimized for the preconcentration of U(VI) from ground water and seawater, and also for the preconcentration of Pu(IV) from 3 mol L−1 HNO3, which is normally encountered in nuclear fuel reprocessing facilities. The parameters affecting the analytical performance of polymer sorbent based TIMS were evaluated, and tested for the quantification of U and Pu in the ppb concentration range in seawater and urine samples using the isotope dilution method.

Phosphate-bearing polymer grafted glass for plutonium(IV) ion-selective alpha spectrometry

A phosphate-bearing polymer thin film was covalently anchored on a glass substrate for alpha spectrometric determination of Pu4+ ions in aqueous samples. This method combined matrix elimination, preconcentration and source preparation into one-step sample manipulation. The thin polymer film was formed by first coupling 3-(trimethoxysilyl)propyl acrylate (TMSPA) on a hydrolyzed glass substrate by a sol–gel process, and simultaneously utilizing the double bonds of TMSPA for the UV-initiator-induced graft polymerization of bis[2-(methacryloyloxy)ethyl] phosphate monomers. The thin phosphate ligand bearing the thus formed poly(bis[2-(methacryloyloxy)ethyl] phosphate) (poly(BMEP)) film was characterized for homogeneity, physical morphology, and its affinity toward representative actinide ions such as UO22+, Am3+, Th4+ and Pu4+ in a HNO3 medium. Alpha track radiography and elemental mapping of the C and P atoms indicated uniform formation of the poly(BMEP) film on the glass substrate. Atomic force microscopy indicated a 10–15 nm thickness of the film, and the alpha spectrum of Pu4+-loaded glass@poly(BMEP) exhibited well defined alpha energy peaks without any significant loss of energy in the host matrix. The glass@poly(BMEP) film was found to sorb Pu4+ ions preferentially in 3 mol L−1 HNO3 in the presence of competing UO22+ and Th4+ ions. Am3+ ions did not sorb to a significant extent under similar conditions, even in the absence of Pu4+ ions. The Pu4+ ions loaded on the glass@poly(BMEP) substrate were quantified by isotope-dilution alpha spectrometry. This glass@poly(BMEP)-based alpha spectrometric method was applied successfully to quantify Pu in aqueous samples. The concentrations of Pu measured by this technique were reproducible within ±6% and required a minimum preconcentration of 2.95 Bq Pu activity in the glass@poly(BMEP) film. The measured Pu concentrations showed good agreement with those obtained by standard thermal ionization mass spectrometry.

Isotopic correlation for 242Pu composition prediction: Multivariate regresssion approach

Multivariate regression calibration using multiple linear regression (MLR), principle component regression (PCR) and partial least squares regression (PLSR) algorithm was performed on 238Pu, 239Pu, 240Pu and 241Pu atom% abundances to predict 242Pu isotopic abundance. The MLR algorithm was found to be the best among these three algorithms. The effect of 238Pu composition on the 242Pu abundance prediction was found to be small but significant especially for achieving high accuracy of <0.5%. PCR and PLSR generated nearly identical results and were inferior to the MLR results. A comparison of MLR results with those obtained by employing seven previously reported empirical methods revealed far superior prediction capability of MLR model. Among the seven empirical models, the best prediction capability was found for Bignan correlation containing 238Pu isotopic data. The study clearly demonstrates that the production of 238Pu and 242Pu has some small correlation and the use of 238Pu in isotopic correlation for 242Pu prediction is important to get accurate results.